I agree - parchment paper is key. I've learned that the only way cakes/brownies/etc come out of a pan clean every time is to 1) grease/butter the pan, 2) lightly flour over the butter and tap out extra, and 3) cut a square of parchment to fit the bottom of pan. A bit of a PITA, but worth it!

I use Baker's Joy for everything that isn't baked on a cookie sheet. Just give the pan a good spray, focusing on the corners. I like it better than butter/flour because it's quicker and I never miss any spots!

Another resounding YES for parchment paper. I let it hang over the side of the pan so that I'm able to lift everything out together once the bars have cooled. I don't find that flour is needed personally, but lightly greasing the parchment seems to help make sure that it sticks down.

I have also seen square pans made with removable bottoms, like this one, but I've never owned one.

parchment paper. definitely.let it hang over the edges, and don't even try to remove them until they're completely cooled.
parchment paper and wax paper are not the same thing.

I've used the Cooks Illustrated method and never had a problem. It involves folding tin foil to fit the pan and making sure lots is left over the sides so you can grab from both ends and lift out, you also coat with non stick spray. Comes out like a charm every time.

Use a bench scraper to cut and remove the bars. After I cut the bars (also with the bench scraper-- it's so much easier than with a knife), I wedge the scraper along the sides to loosen and lift the pieces out. I can get right under the bars and pull them up with more ease than with a spatula.

Also, chilling the pan makes it harder to remove the bars; a slightly warm pan will make it easier to get them out, even if it means popping the pan back in the oven for 5 minutes to warm it slightly.

Thumbs up for parchment paper with the ends hanging out. Plus once you get it out of the pan, it makes it easier to cut.

Try non-stick aluminum foil. It's a miraculous substance. Even baked macaroni and cheese doesn't stick to it. I almost never bother with parchment paper now.

I second the tinfoil method of turning the pan over, molding the foil to the pan and then flipping the pan and tucking the tin foil into it. Butter it and make sure there is some foil to use as handles to lift them out and cut. Oh — and put the foil in the pan so that the dull side is up.

parchment, parchment, parchment.

also: the reason i avoid foil is it can change the way something bakes. i do most of my baking in Pyrex, and adding a reflective surface changes the behavior of the pan. it might not be a drastic enough change for most people, but i'm a stickler for perfection, and i find foil can make things less predictable.

Pastry shop I used to work at used parchment and I'm almost positive they buttered it - either that or there was a TON of butter in that shortbread crust, because although sometimes the paper stuck, it was often so well-greased it was the grease keeping it stuck to the bars.

Also, cutting the bars IN the pan can help - that's what we always did. Then you can lift out individual bars, so they're less likely to break. Of course, you ruin aluminum pans and knives eventually, but parchment helps mitigate the wear on the pans.

If you have a shortbread crust, its mostly butter so no real need to grease the paper but DEFINITELY use parchment with overhang and a big one no one said- with lemon bars the key to a crisp crust and all that is make sure your edges has a lip of crust so the filling doesn't run down the sides and leach under the crust. It can become like glue if you do and make it nearly impossible to get out clean even with parchment. I love the tip of baking the crust I then opening the oven and pouring the lemon right on top without touching it. You guarantee it wouldn't splash over.